This invention relates to the drying of granular materials such as welding flux, and particularly to an apparatus and method for drying such flux.
It is known that fluxes fo submerged arc welding, and particularly those of the basic type, are hygroscopic. This is, the fluxes take up moisture from the ambient atmosphere during storage. As it is important for proper functioning of the fluxes that they be dry when used, technical specifications regarding the use of such fluxes prescribe drying of the fluxes before use so that the moisture content at use corresponds to that which was present when the flux was packaged by the manufacturer.
Redrying must be carefully done in order to avoid altering the granular characteristics of the flux. In accordance with certain procedures which have been specified heretofore, drying was accomplished in a drawer type oven at a temperature range between 250.degree. and 400.degree. Celsius for a time interval of two hours and with a maximum flux depth of 100 millimeters. After drying, the flux is to be held at a temperature of 150.degree. Celsius. In these procedures, migration of moisture to the surface and diffusion from the granular flux requires substantial time and drying is thus relatively slow.
Alternate forms of ovens have been proposed in which granular material is fed downwardly through a hollow staft mounted at an angle or passed over heated plates or bars by vibration. In such ovens, drying conditions for the flux are often non-uniform and uncontrollable due to variations in depth of the flux material within the furnace. Further, the holding times of flux within the oven are relatively short, and it becomes difficult to dry a flux (particularly a more highly absorbtive one) to the original condition.